Set of Iron Clubs with Constant Ground Roll

ABSTRACT

A set of iron clubs where each club in the set has the same or substantially the same ground roll. The set is produced by adjusting at least two club design characteristics of the clubs based upon measured or assumed player swing data. The design characteristics of the clubs include club length, static clubhead loft, location of the center of gravity, shaft flexibility, and groove volume. Preferably, club length and static clubhead loft are adjusted for coarse adjustments, while the other characteristics are used to fine-tune the design.

BACKGROUND

The invention relates generally to a set of iron-type golf clubs. Inparticular, the invention relates to a set of irons with substantiallyconstant ground roll.

In a set of irons, various design characteristics are varied from oneclub to the next. For example, individual iron club heads in a settypically increase progressively in face surface area and weight as theclubs progress from the long irons to the short irons and wedges. Theshaft length shortens as the clubs progress from the long irons to thewedges, and the loft angle typically increases through the sameprogression. These design variables and others can be modified so that aparticular club, for example a 3-iron, produces certain flightcharacteristics. Specifically, the clubs are designed to producespecific launch angles and to impart a certain amount of backspin to theball, when the ball is struck correctly, i.e., with an anticipated speedand at the nominal hitting point, typically a point on the hitting faceabout 18 mm or less above the ground when the club is in the addressposition. When struck in the appropriate manner, the combination of ballspeed, launch angle and backspin produces an anticipated flight path,with the ball achieving a specific height at the maximum point of theparabolic arc of the path and a specific carry distance.

In traditional iron sets, flight path height (distance above ground) andcarry distance are generally the performance parameters which a golfclub is designed to achieve. However, another parameter, ground roll ofthe ball, is relatively neglected in the overall design of the club,with ground roll being dependent upon the design characteristicsselected to achieve a specific flight path. As such, traditional ironsets result in longer shots having the ball roll more on a green than dothe shorter shots. This creates difficulty in hitting long shots whichwill stop on a green. Also, some short shots can roll backwards on thegreen. As a result, precisely controlling the total distance achieved bya shot may prove difficult if the player cannot accurately account forground roll distance. A shot hit with a club from an iron set would beeasier to control, i.e., the distance attained for a shot from each ironwould be more predictable, if each would roll a prescribed distance.

Therefore, a need exists for a set of iron clubs having predictableground roll. Such a set of clubs may have the same ground roll for eachclub in the set.

SUMMARY OF THE INVENTION

An aspect of the invention is directed toward a set of iron-type clubscomprising at least two clubs, wherein a ground roll distance producedby each of the at least two clubs is substantially the same.

Another aspect of the invention is directed toward a method forproducing a set of golf clubs with constant ground roll comprising thesteps of (i) selecting a target ground roll, (ii) selecting a club,(iii) obtaining a ground roll performance curve for the club and atleast one other performance curve using the club, and (iv) adjusting atleast two design characteristics of the club to achieve the targetground roll while maintaining the at least one other performance curve.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic view of a standard iron club;

FIG. 2 is a graph showing the variation in clubhead speed versus clublength for a typical PGA Tour player;

FIG. 3 is a graph showing the variation in carry distance versus clublength and static club loft for 3-irons;

FIG. 4 is a graph showing the variation in ground roll versus clublength and static club loft for 3-irons;

FIG. 5 is a graph superimposing the graph of FIG. 4 onto the graph ofFIG. 3;

FIG. 6 is a graph showing the variation in ground roll and carrydistance versus club length and static club loft for 6-irons;

FIG. 7 is a graph showing the variation in ground roll and carrydistance versus club length and static club loft for 9-irons;

FIG. 8 is a graph showing the variation in clubhead static loft versusiron number for three sets of iron-type golf clubs, one conventional setand two constant roll sets;

FIG. 9 is a graph showing the variation in club length versus ironnumber for three sets of iron-type golf clubs, one conventional set andtwo constant roll sets; and

FIG. 10 is a graph showing the variations in flight trajectories forconventional and constant roll 3-, 6-, and 9-irons.

DETAILED DESCRIPTION

As illustrated in the accompanying drawings and discussed in detailbelow, the present invention is directed to a set of iron-type golfclubs, wherein the clubs have substantially the same ground rolldistance throughout the set. Each club 1 in a set includes a club head10 attached to a tubular portion 18 of a shaft 17 in any manner known inthe art, such as with an adhesive, welding, or screwing threadedportions of club head 10 to a correspondingly threaded portion oftubular portion 18. The length of club 1 is determined by measuring froma grip or handle portion 19 of shaft 17 to a sole 22.

Club head 10 includes, generally, a body 12 and hosel 14. Body 12includes a striking or hitting face 16 and a rear face 20. Body 12 isattached to hosel 14 at an angle, such that a loft angle 30 is definedbetween a hosel center line 18 and hitting face 16. Further, therelative configuration of body 12 and hosel 14 results in an offset 34between the leading edge of the base of sole 22 at the base of hittingface 16 and the forward-most point 15 of hosel 14.

In typical sets of golf clubs, the area of hitting face 16, theheel-to-toe length of body 12, loft angle 30, and offset 34 vary fromclub to club within the set. For example, long irons, such as a 2- or3-iron using conventional numbering, typically include relatively longshafts 17, relatively small areas for hitting face 16, and relativelylow loft angles 30. Similarly, short irons, such as an 8- or 9-ironusing conventional numbering, typically include relatively short shafts17, relatively large areas for hitting face 16, and relatively high loftangles 30. In one embodiment of the present invention, these parametersare particularly chosen to maximize the performance of each club 1 forits intended use in terms of carry distance.

The total distance achieved by a ball struck by a club is the carrydistance plus the distance the ball rolls upon landing, also referred toas “ground roll”. Ground roll is generally influenced by initialconditions of the ball upon impact, such as launch speed, launch angleand back spin. Many factors influence the ground roll distance,including club design characteristics and player swing characteristics.In a set of clubs according to the present invention, the designparameters of the clubs in the set and/or the player swingcharacteristics are matched and selected not only to maximize theperformance of each club for its intended use, for example as a wedge,but also to achieve a predictable level of ground roll of a ball struckby any club in the set, such as constant or substantially constantground roll.

In accordance with an aspect of the present invention, the inventiveiron golf clubs are designed to have substantially the same carrydistance as conventional iron golf clubs. Each inventive iron golf clubis designed to hit golf balls a prescribed distance in the air, and tostop on the green or fairway in a predictable manner. Expected groundroll distances for conventional irons ranges from about 6 yards for a3-iron, 2 yards for a 6-iron and 0 yards (or less) for a 9-iron. Hence,it is difficult for a player to make the ball stop on the green with a3-iron. The present invention includes a method for creating a set ofiron clubs that has substantially the same ground roll for each club,while maintaining the same carry distance as the conventional clubs.Preferably, each club should have the same ground roll distance ±1 yard.

Using actual golf ball launch data, the carry distance and ground rollare calculated using a mathematical model. First, a targeted ground rollis selected, i.e., 2 yards±1 yard. Next, adjustments are made to adjustthe ground roll to reach the target roll. For example, if the datasuggest that the landing roll for a particular club is longer than thetarget ground roll, then adjustments are made to reduce the roll.Adjustments include, but are not limited to, the following factors:

-   -   i. increasing/decreasing shaft length to adjust clubhead speed        and initial ball speed;    -   ii. increasing/decreasing static loft angle to adjust trajectory        and backspin;    -   iii. flexing characteristics of the shaft to adjust clubhead        speed and initial ball speed;    -   iv. location of the center of gravity (c.g.) of the clubhead,        including lowering the c.g. and/or moving the c.g. aft of the        hitting face, to adjust trajectory of the ball; and    -   v. varying groove geometry to adjust the amount of ball spin

A high launch/high spin combination makes the ball fly higher andreduces carry and roll distances. In one example, higher trajectory iscoupled with longer shaft length (or shaft flex) to increase ball speedto make up for the loss of carry distance, but to keep the ground rollunchanged. Hence, in this example, after the adjustments the clubmaintains its expected carry distance while the ground roll distance hasbeen adjusted to meet the targeted roll distance. This method isrepeated for each club in the set to achieve the same targeted rolldistance for all the clubs.

In accordance with one aspect of the present invention, at least two ofthe above five club factors are used to reach the targeted ground roll.It is noted that other factors may be used for this purpose.

The properties of the golf balls may also affect the targeted groundroll. For instance, the ball's compression, total hardness, covermaterial, and dimple pattern, among other factors, can affect both thecarry distance and roll distance. The ball launch data includes multipletypes of golf balls. Hence, the mathematical model is applicable to allgolf balls, and the inventors expect that when the inventive iron golfclubs are used with a particular ball, the targeted ground roll distanceremains the same throughout the set. However, the targeted ground rollmay be different for different balls. For example, a higher performancegolf ball such as the Titleist Pro-V1® or Pro-V1x™ would produce onetargeted ground roll distance for the inventive set, while another ballwould produce another targeted ground roll distance for the inventiveset.

Discussed further below is an understanding of the players' swingcharacteristics, such as clubhead speed, angle of attack, loft at impactand nominal impact position. One of these player swing characteristicsthat impacts ground roll is the angle of attack, i.e., the angle betweenthe path on which the clubhead strikes the ball and the horizontalground plane. A typical forward swing for a golfer follows an arc,starting with a downswing, traveling through a fairly level portion atthe bottom of the downswing before heading into the upswing part of theswing. Typically, the angle of attack for irons in generally downward,i.e., the ball is struck in the downswing portion of the swing arc. Asthe angle of attack becomes more level, the launch angle increases andthe backspin decreases. The nominal impact location also affects theflight path. An ideal nominal impact location, the striking point on thehitting face of a club, is about 18 mm or less measured from ground whenthe club is in the address position. In the absence of ground contact,“thin” hits, hits lower than the nominal striking point, decrease thelaunch angle of a ball, and “fat” hits, hits higher than the nominalstriking point, increase the launch angle of a ball.

In one embodiment of the present invention, club design characteristicsare manipulated based upon assumed or measured player swingcharacteristics to achieve constant ground roll through the set. Inother words, clubs of the set are designed so that a ball struck by anyclub in the set rolls the same distance, regardless of which club in theset is used to strike the ball. To achieve this effect, in oneembodiment a set is designed so that each club, for example, a 3-iron,has the same or nearly the same flight trajectory as its conventionalcounterpart while ground roll remains constant. In a first embodiment,the club design parameters are chosen based upon a typical PGA Tourplayer's swing, where the model for the characteristics of the swing isderived from empirical data collected from a number of actual PGA Tourplayers. In another embodiment, a custom set may be developed bycollecting data from an individual player and adjusting the club designparameters to match the swing characteristics of that specific player inorder to achieve constant roll through the set. An individual's customlaunch measurements can be obtained easily during a standard fittingsession using a launch monitor system, such as the Titleist performancemonitor (TPM).

As discussed above, one club design characteristic that may bemanipulated to influence ground roll is the clubhead speed. A playerwill swing a club with a certain amount of strength and skill to achievea player-dependent swing speed. While swing speeds may vary widely amongthe general population, swing speed for PGA Tour players tends to beconsistent and will fall within a relatively narrow range for a givenclub. For instance, it is uncommon for a PGA Tour player to swing a3-iron outside of the 95 mph to 105 mph range, whereas anon-professional could easily fall well below the 100 mph mark. It isknown in the art that clubhead speed also varies with club length givena certain swing speed, so the clubhead speed may be manipulated tocontrol ground roll by altering the club length. FIG. 2 showsgraphically how the clubhead speed of a club swung by an average PGATour player varies with club length for a conventional set of irons. Theaverage clubhead speed variation with club length, as determined fromthe data shown in the graph of FIG. 2, is about a 2.35 mph increase inclubhead speed per 1 inch increase in club length. The correspondingincreases in ball speed per 1 inch increase in club length for 3-, 6-,and 9-irons are shown below in Table 1.

TABLE 1 Increase in Ball Speed Given a 1-inch Increase in Club LengthClub Number Increase in Ball Speed (mph) 3 3.17 6 3.03 9 2.80As clubhead speed increases, the initial velocity of the ball uponimpact is also increased. As such, the ball will tend to have a greatercarry distance and greater ground roll with increased clubhead speed, asis shown and discussed in greater detail below in the Example.

As the clubhead speed increases, so does the backspin imparted to theball. Backspin, the backward rotation of the golf ball in flight alongits horizontal axis, is imparted to the ball by the grooves formed inthe hitting face of a club and friction between the ball and thestriking face. When struck, the ball compresses into and slides alongthe hitting face, encountering the grooves. A tangential force isimparted to the ball which causes the backward rotation of the ball. Asis well known in the art, backspin produces aerodynamic lift for greatercarry distances. Also, backspin influences ground roll by slowing,stopping or even reversing the direction in which the ball is travelingwhen the ball hits the ground. In other words, ground roll is shorter oreven backwards with greater backspin. Backspin generally increases withclubhead speed. Table 2 shows the increase in backspin for a 1 mphincrease in clubhead speed for selected clubs from a set of muscle-backclubs, assuming a PGA Tour player swing hitting a Titleist® ProV1x™ball.

TABLE 2 Increase in Backspin of a 1 mph Increase in Clubhead Speed ClubIncrease in Backspin (revolutions per minute) 3-iron +40 rpm 6-iron +58rpm 9-iron +88 rpm

Backspin also generally increases with static clubhead loft, i.e., theloft angle (element 30 in FIG. 1) of the club as measured when the clubis in the address position. As loft angle increases, backspin increases.Static loft also impacts initial ballspeed, which decreases, withincreasing static clubhead loft. Therefore, as the static loftincreases, the ground roll decreases through a combination of lowerballspeed and increased backspin, as discussed above. Launch angle alsoaffects ground roll, as ground roll generally decreases with increasedlaunch angle. Table 3 shows the changes in ballspeed, backspin andlaunch angle for a 1 degree increase in static loft for selected clubsfrom a set of muscle-back clubs, assuming a PGA Tour player swinghitting a Titleist® ProV1x™ ball.

TABLE 3 Per Degree Change in Ballspeed, Backspin and Launch AngleIncrease in Static Loft Change in Backspin Change in Ballspeed(revolutions Change in Launch Club (miles per hour) per minute) Angle(degrees) 3-iron −0.83 mph   +251 rpm +0.71° 6-iron −1.15 mph +242.8 rpm+0.67° 9-iron −1.16 mph +191.8 rpm +0.63°

Additional design characteristics which impact carry distance and groundroll include those design characteristics which impact launch angle. Forexample, the position of the center of gravity of the club influenceslaunch angle, where a center of gravity closer to the sole of theclubhead increases the initial launch angle. Additionally, increasedflexibility of the shaft also increases the initial launch angle.Further, the geometry of the grooves impacts backspin, withlarger-volume and sharper radius grooves imparting greater backspin.

For the purposes of designing a set of constant ground roll clubsaccording to the present invention, the design of a conventional set ofclubs with the desired flight path characteristics may be provided as abasic starting point. Alternatively, a set of clubs may be independentlydesigned to obtain a set of clubs with the desired flight pathcharacteristics. For the purposes of simplicity in the discussion, theset used as the basic starting point is referred to as “the conventionalset” even if the set is specifically designed. Any two or more of theabove-discussed parameters may be manipulated or slightly varied inorder to substantially maintain the flight path characteristics of theconventional set, in particular the carry distances and/or thedifference in carry distance from one club to the next in the set, whileobtaining the desired constant or substantially constant ground roll.Preferably, club length and loft angle are the parameters which arevaried from the conventional set, although any combination of parametersmay be adjusted. Club length and loft angle are preferred in partbecause relatively minor changes in these parameters have a greaterimpact on carry distance and ground roll than do the other parametersdiscussed herein. In other words, club length and loft angle can be usedfor coarse corrections to carry distance and ground roll, whileparameters such as shaft flexibility, groove volume, and center ofgravity locations can be used to fine-tune carry distance and groundroll.

In one example, a set of constant ground roll clubs according to thepresent invention were predicated off of the design of a conventionalset of iron clubs, the Titleist® 670. In other words, the flight pathcharacteristics of the conventional set were chosen as desirable flightpath characteristics. In order to achieve the same or similarcharacteristics, the conventional set's general overall design wasmaintained, while each club's length and loft angle were manipulated toproduce the desired ground roll. In this example, it is desired to haveall clubs roll to within one yard of the ground roll achieved by theconventional set 6-iron, although one of skill in the art will recognizethat any ground roll may be selected as the target ground roll. In otherwords, if the 6-iron of the conventional set has a ground roll of 2yards, the inventive set iron should have a ground roll between about 1yard to about 3 yards. The conventional set is a muscle-back type ironmade from forged steel. The conventional set 3-iron, 6-iron and 9-ironsall have similar centers of gravity, both as measured from the groundwhen the club head is in the address position and as measured from apoint on the hitting face about 15 mm above the ground when the club isin an address position.

As discussed above, it is preferred that the clubs of the conventionalset are adjusted by slightly varying club length and static clubheadloft in order to obtain the inventive constant roll set. FIG. 3 showshow carry distance is affected by static clubhead loft and club length.Point A on FIG. 3 indicates the distance traveled by a 3-iron of theconventional set, which has a static clubhead loft of 22° and a clublength of 39 inches. Isobars B show carry distance performance curves in10-yard increments, with carry distance increasing generally as clublength increases. As shown, increasing only the club length of the3-iron of the conventional set by one inch (to 40 inches) increases thecarry distance by about 5 yards, and decreasing only the club length ofthe 3-iron of the conventional set by one inch (to 38 inches) decreasesthe carry distance by about 5 yards. Similarly, increasing only thestatic clubhead loft by one degree (to 23 degrees) decreases the carrydistance by about 4 yards, and decreasing only the static clubhead loftby one degree (to 21 degrees) increases the carry distance by about 3yards. Therefore, manipulating both parameters results in relativelylarge changes in carry distance. For example, by increasing the clublength of the 3-iron of the conventional set by one inch (to 40 inches)and decreasing the static clubhead loft by one degree (to 21 degrees), acarry distance increase of about 10 yards can be achieved. Similarly, bydecreasing the club length of the 3-iron of the conventional set by oneinch (to 38 inches) and increasing the static clubhead loft by onedegree (to 23 degrees), a carry distance decrease of about 9 yards canbe achieved.

FIG. 4 shows how ground roll is affected by static clubhead loft andclub length. Point C on FIG. 4 indicates the ground roll of a 3-iron ofthe conventional set. Isobars D show ground roll performance curves in2-yard increments, with ground roll increasing generally as staticclubhead loft decreases. As shown, increasing only the club length ofthe 3-iron of the conventional set by one inch (to 40 inches) decreasesthe ground roll by about ½ yard, while decreasing only the club lengthof the 3-iron of the conventional set by one inch (to 38 inches)increases the ground roll by about ½ yard. Further, increasing only thestatic club loft by one degree (to 23 degrees) increases the ground rollby about one yard, while decreasing the static club loft by one degree(to 21 degrees) decreases the ground roll by about one yard. As such,manipulating both parameters results in relatively large changes inground roll. For example, by increasing the club length of the 3-iron ofthe conventional set by one inch (to 40 inches) and increasing thestatic clubhead loft by one degree (to 23 degrees), a ground rolldecrease of about 1.5 yards can be achieved. Similarly, by decreasingthe club length of the 3-iron of the conventional set by one inch (to 38inches) and decreasing the static clubhead loft by one degree (to 21degrees), a ground roll increase of about 1.5 yards can be achieved.

FIG. 5 shows how simultaneous changes in static clubhead loft and clublength affect both ground roll and carry distance, assuming an averagePGA Tour player swing, by overlaying a portion of the graph of FIG. 3onto the graph of FIG. 4. Isobars D show ground roll differentials of 2yards, with Isobar D′ showing the target ground roll. Isobar G shows thecarry distance of the 3-iron of the conventional set. Point E on FIG. 5indicates the carry distance and ground roll of the 3-iron of theconventional set. By following Isobar G to the desired ground roll pointon Isobar D′, as indicated by Point F, the club length and staticclubhead loft that will produce the target ground roll can be determinedwhile holding all other design parameters constant and maintaining thedesired carry distance. As such, to decrease the ground roll of the3-iron of the conventional set to the target ground roll, the staticclubhead loft is increased to nearly 26 degrees and the club length isincreased to about 41 inches.

FIG. 6 is similar to FIG. 5 in that it shows how simultaneous changes instatic clubhead loft and club length simultaneously affect ground rolland carry distance, assuming an average PGA Tour player swing. However,FIG. 6 shows these changes for a 6-iron of the conventional set. IsobarsI show ground roll differentials of ½ yard, with Isobar D′ showing thetarget ground roll point. Isobars H show carry distance differentials of15 yards. Isobar J reflects the carry distance of the 6-iron of theconventional set. Point L on FIG. 6 indicates the carry distance andground roll of the 6-iron of the conventional set, a 37.5 inch club witha static clubhead loft of 32 degrees. By following Isobar G to thedesired ground roll point on Isobar D′, as indicated by Point K, theclub length and static clubhead loft that will produce the target groundroll can be determined while holding all other design parametersconstant and maintaining the desired carry distance. As such, toincrease the ground roll of the 6-iron of the conventional set to thetarget ground roll, the static clubhead loft is decreased to about 31.7degrees and the club length is decreased to about 37.3 inches. Notably,the adjustments to the club length and static clubhead loft for the6-iron are relatively minor as compared with the changes made to the3-iron in order to obtain the same ground roll for both clubs, as thedesired ground roll is closer to the ground roll of the conventional6-iron than the conventional 3-iron. As such, it would be appropriate touse the conventional 6-iron as the 6-iron of the inventive set, to avoidre-tooling or redesigning the club while still having approximately thesame amount of ground roll as the rest of the set.

FIG. 7 is similar to FIGS. 5 and 6 in that it shows how changes instatic clubhead loft and club length simultaneously affect ground rolland carry distance, but for a 9-iron, assuming an average PGA Tourplayer swing. Isobars M show ground roll differentials of ½ yard,increasing in distance with decreasing club length, with Isobar D′indicating the desired ground roll for the inventive set. Isobars N showcarry distance differentials of 20 yards, generally increasing withincreasing club length. Isobar O reflects the carry distance of the9-iron of the conventional set. Point P on FIG. 7 indicates the carrydistance and ground roll of the 9-iron of the conventional set, a36-inch club with a static clubhead loft of 25 degrees. By followingIsobar O to the desired ground roll point, as indicated by Point Q onIsobar D′, the club length and static clubhead loft that will producethe target ground roll can be determined while holding all other designcharacteristics constant and maintaining the desired carry distance. Assuch, to increase the ground roll of the 9-iron of the conventional setto the desired level reflected by Isobar M′, the static clubhead loft isdecreased to about 38 degrees and the club length is decreased to about32 inches. As this point remains on Isobar O, the carry distance remainsthe same for the inventive 9-iron as the conventional 9-iron. As will berecognized by those in the art, the club length for the 9-iron may beshorter than is comfortably played for many players. Therefore, it iswithin the scope of the invention to lengthen the 9-iron, such as to amore comfortable 34.125 inches. As the target ground roll need only bewithin one yard of the ground roll identified by Isobar M′, a staticloft of about 42 degrees may be selected to achieve a ground roll withintolerances.

While only 3-, 6-, and 9-irons are discussed above, similar analysis anddesign can be done for each club in a set to achieve constant or nearlyconstant ground roll for each club in the set. FIGS. 8 and 9 show theselected static lofts (FIG. 8) and club lengths (FIG. 9) for theconventional, ideal constant roll and nearly constant roll sets. In FIG.8, curve 120 indicates the static lofts of the conventional set. Curve122 indicates the static lofts of an inventive set that perfectlyfollows the graphs discussed above, while curve 124 indicates the staticlofts of a preferred set which accounts for both nearly constant groundroll within the desired tolerances and other aesthetic considerations,such as a longer 9-iron than would be found in a set that strictlyfollows the determinations of the performance curves, as discussedabove. In FIG. 9, curve 126 shows the club lengths for the clubs of theconventional set, while curve 128 shows the club lengths for theconstant roll set. Curve 130 shows the preferred club lengths for thenearly constant roll set. As shown in FIG. 9, the club lengths of thenearly constant roll set more closely resemble those of the conventionalset than do the clubs of the constant roll set.

As such, the desired carry distances for the inventive 3-, 6-, and9-irons remain the same as those of the conventional 3-, 6-, and9-irons, respectively, while each club in the inventive set produces thesame or nearly the same ground roll. This added level of predictabilityis reflected in FIG. 8, which shows the trajectories achieved by theinventive and conventional sets. The trajectory of the conventional3-iron is indicated by line 100, with the inventive (constant roll)3-iron trajectory indicated by trajectory 102. Both 3-irons, as struckby an average PGA Tour player, achieve the same downrange distance, withthe conventional 3-iron having a higher maximum height above ground.Trajectory 104 indicates the trajectory of the conventional 6-iron, andtrajectory 106 indicates the trajectory of the inventive 6-iron. As withthe 3-irons, the same downrange distance is achieved with both 6-irons,with the conventional 6-iron having a slightly higher maximum heightabove ground than the inventive 6-iron. However, as discussed above, theconventional 6-iron produces a ground roll very similar to the targetground roll, so the conventional 6-iron may be used in the inventiveset, in which case trajectories 104 and 106 would be exactly the same.Finally, trajectory 108 indicates the trajectory of the conventional9-iron, and trajectory 110 indicates the trajectory of the inventive9-iron. As with the irons discussed above, the same downrange distanceis achieved with both 9-irons, with the conventional 9-iron having aslightly higher maximum height above ground than the inventive 9-iron.

While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objectives of the present invention, it isappreciated that numerous modifications and other embodiments may bedevised by those skilled in the art. Additionally, feature(s) and/orelement(s) from any embodiment may be used singly or in combination withfeature(s) and/or element(s) from other embodiments. Therefore, it willbe understood that the appended claims are intended to cover all suchmodifications and embodiments, which would come within the spirit andscope of the present invention. All publications discussed herein,including but not limited to patents, patent applications, articles, andbooks, are incorporated by reference in their entireties.

1. A set of iron-type clubs comprising at least two clubs, wherein aground roll distance produced by each of the at least two clubs issubstantially the same.
 2. The set of clubs of claim 1, wherein theiron-type clubs are muscle-back clubs.
 3. The set of clubs of claim 1,wherein the ground roll distance of each of the at least two clubs iswithin one yard of a target ground roll distance.
 4. The set of clubs ofclaim 1, wherein one of the at least two clubs has a first club lengthof between about 38 inches and about 42 inches and a static clubheadloft of between about 25 degrees and 27 degrees, and wherein the otherof the at least two clubs has a second club length of between about 32inches and about 35 inches and a second static clubhead loft of betweenabout 38 degrees and about 42 degrees.
 5. The set of clubs of claim 4further comprising at least one additional club having a third clublength of between about 37 inches and about 39 inches and a third staticclubhead loft of between about 30 degrees and about 33 degrees. 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled) 11.(canceled)
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)16. (canceled)
 17. (canceled)
 18. A set of iron-type clubs comprising atleast two clubs, wherein a ground roll distance produced by each of theat least two clubs is substantially the same, wherein a first club is a3 iron having a loft of about 25 degrees and a shaft length of about 41inches and a second club is a 9 iron having a loft of about 40 degreesand a shaft length of about 34 inches and the remaining clubs within theset have lofts and shaft lengths therebetween.